1. Field of the Invention
The present invention relates to a motor control device for use in a camera system having two motors one for driving a photographic lens for an automatic focus control and the other for sequence control of the camera system.
2. Description of the Prior Art
In a camera having automatic focus function, there are provided a lens motor for shifting a photographic lens for the automatic focus control and a sequence motor for winding a film and controlling a mirror, that is, two motors must be installed in a camera. A conventional driver controller for driving said two motors is shown in FIG. 13 in which reference numerals M.sub.1 and M.sub.2 denote respectively the sequence motor for winding a photographic film and lens motor and Q.sub.1 to Q.sub.4 and Q.sub.5 to Q.sub.8 denote respectively transistors for driving the motors M.sub.1 and M.sub.2. The respective transistors Q.sub.1 to Q.sub.4 and Q.sub.5 to Q.sub.8 are arranged in the bridge circuit. Reference numerals D.sub.1 to D.sub.4 denote respectively diodes for absorbing a voltage applied in the direction opposite to the normal direction.
In operation, for example, the motor M.sub.1 rotates in the forward direction when the transistors Q.sub.1 and Q.sub.4 are on and the transistors Q.sub.2 and Q.sub.3 are off, and the motor M.sub.1 rotates in the reverse direction when the transistors Q.sub.1 and Q.sub.4 are off and the transistors Q.sub.2 and Q.sub.3 are on.
In the driver as mentioned above, eight power transistors with large capacity are needed and eight control lines shown as P.sub.1 to P.sub.8 are needed for controlling the transistors Q.sub.1 to Q.sub.8 in the driver controller, so that there is a drawback that a space for installing the transistor circuit in a control substrate becomes large.
Besides the above problem, in case of controlling a load having large current capacity such as a sequence motor for winding a photographic film and an electromagnet for shutter control under the control of a microcomputer, a power drive circuit is generally provided between the output terminals of the microcomputer and the loads because of the lack of the driving capacity of the microcomputer.
In case the number of the loads to be driven is small, the respective driving circuits may be formed by discrete systems, but, in case a lot of drive circuits are used it is desired to form the respective driving circuits in an IC chip. In this case, assuming to use four loads, for example, eight output terminals from the IC chip are needed and four output terminals of the microcomputer are needed in order to control the IC chip. Therefore, there is a problem that the number of output terminals of the IC chip is less than as needed, or the manufacturing cost increases because a special design is needed for the IC, or the substrate of the IC becomes complicated due to increase of the control lines.
Hence, the number of the control input terminals of the IC should be decreased and there have been produced various kinds of driving IC which can control four states of forward rotation, reverse rotation, brake and stop of the motor using two input terminals of the IC. However, all of the conventional IC can control only one load and there has not been known any IC which can control a plurality of loads simultaneously.